Sander drum



Aug. 16, 1955 A. L. THoRsoN ET A1. 2,715,303

SANDER DRUM Filed June 5, 1949 IN VEN TORS- //zeg 7720219072,

United States Patent SANDER DRUM Arnett L. Thorson and Louis C. Nolte, Chicago, Ill.

Application June 3, 1949, Serial No. 97,046

7 Claims. (Cl. 51-194) This invention relates generally to sanding machines and more particularly to an improved power-driven iloor sander.

Although the sanding machine disclosed which embodies this invention is intended primarily for use in finishing oors, many of the novel features of the invention incorporated therein may be used in other types of sanding machines such as the hand models used in nishing furniture, walls, boats, etc., and stationary Sanders where the work is moved over the sander.

In sanding oors it is essential that the sandpaper be frequently replaced during the sanding operation, not only to substitute new sheets for those which have had the abrasive surface worn off or caked with varnish and the like, but also to change the grade of sandpaper from coarser grades for initial sanding to finer grades for the finishing operation. Although other types are used, the general practice is to mount the sheets on the cylindrical surface of a rotatable drum. To do this, the usual pracw tice has been to provide rectangular sheets of sandpaper which are wrapped around the drum and secured thereto by a clamp-lock device generally comprising a bar or bars of metal extending the length of the drum and functioning as cams or clamps engaging the ends of the sandpaper sheet. The ends are tucked radially inwardly underneath or between the bars and the bars rotated or screwed down. Other arrangements have been provided in which the sandpaper is held in place by various clamping devices which draw the paper tight while locking pressure is applied, but none of these has proved wholly satisfactory in that either the paper does not pull down evenly or becomes askew, or the paper is not securely clamped when installed, and creeps loose. In any event, the best of conventional clamps should extend parallel with the drum axis, but such permits the drum to bounce and mar the door each time the drum rotates. Clamps arranged helically to avoid this bounce encounter other diticulties of adjustment or use. Much trouble is also encountered by unskilled users not being able to understand the operation of the sandpaper securement devices because they cannot see or understand how they operate. Misuse or carelessness results.

Another difficulty encountered resides in certain characteristics of the sandpaper itself. Sandpaper is likely to become wrinkled or the abrasive surface broken during installation on the drum, thereby producing an irregularity which mars the surface of the floor or introduces a tear in the paper as the drum rotates.

Most of the conventional locking devices require tool access at the ends of the drum if multiplicity of adjustments is to be eliminated. This interferes with compactness and transmission drives and requires an arrangement of parts which prevents sanding close to baseboards.

Accordingly, one of the main objects of this invention is to provide a novel, improved arrangement for attaching the sandpaper to the sanding drum by which the sheets may be rapidly changed on the job without the need for special tools or for access to the face ends of the drum,

2,715,303 Patented Aug. 16, 1955 rice and the manner of attachment to Ithe drum is readily apparent to anyone.

A further object is to provide an arrangement whereby the sheets are securely supported on the surface of the drum in such fashion that they cannot become wrinkled, and are self-adjusting and self-tightening during operation, automatically and otherwise.

Another object is to provide an improved form of abrasive sheet, particularly adapted for attachment to the drum of a sander, which is less likely to wrinkle or tear than conventional sheets.

A further object of the invention is to provide a sheet and drum structural arrangement which eliminates all marring of the oor and which will sand to within fractions of an inch of the wall board.

Various other objects and advantages of this invention will present themselves to those familiar with the art on reading the following specification in conjunction with the appended claims and the drawings, in which:

Fig. l is a plan view showing a sanding drum for a sanding machine incorporating a preferred embodiment of the invention;

Fig. 2 is a section of the drum taken on line 3--3 of Fig. l;

Fig. 3 is a section taken on line 4 4 of Fig. 2; and

Fig. 4 is a plan View of the sandpaper sheet embodying features of the invention.

By sandpaper, as used herein and in the claims, is meant any sheet material having abrasive particles or a polishing medium carried by a exible backing such as cloth, paper, skin, sheet material, etc., and includes emery cloth, carborundum paper, and polishers such as felt, wool, and flocculated bers.

=At the front end of the member 1S a cover 20 is attached by a pair of hinges 21 and curved to follow the contour of the side plates. This cover may be swung upwardly to expose the drum 11 in front so that the sandpaper 22 may be readily mounted or removed.

The arrangement by which the novel abrasive sheets 22 are attached to the drum 11 is shown. The drum comprises a pair of circular end plates 70 and 71 which are welded to the ends of a hollow cylinder 72. The end plate 71 projects beyond the end of the cylinder 72 and has the drive pulley 33 formed integrally therewith. The other end plate 70 is flat-sided and flush with the end of the cylinder 72 so that the sanding surface extends substantially to the inside edge of the side plate, permitting sanding quite closely to Walls, eliminating the need for hand finishing the marginal edges of floors.

The outer surface of the cylinder 72 has a sheet of rubber 73 cemented thereto which covers the entire surface except for a small triangular inclined recess 74 at the center thereof. Substantially, at the center of the inclined wall of the triangular recess, a button or hook 75 is provided which projects radially a slight distance from the surface of the inclined wall but not high enough to extend to the surface of the rubber 73. On each end of the drum 11 an inclined slot 76 is provided which extends through the rubber 73 and through the end of the cylinder 72. The two slots 76 are located in line with each other and are circumferentially spaced from the hook 75.

The abrasive sheet 2?. has the shape shown, being cut to a point at one end and having a mating swallow-tail form at the other. A grommet 77 preferably is provided at the pointed end of the sheet 22. To install the sheet 22 on the drum 11, the grommet 77 is slipped over the hook 75, and the drum 11 is rotated to wrap the sheet 22 around it. The two trailing ends or tips 78 of the sheet 22 are then slipped into the slots 76, assuming the position shown in Fig. 8.

After insertion with the cylinder stationary, the two tips 78 are held lightly in the slots 76 by the action of a pair of centrifugal weight elements Sil pressed outwardly by springs 81. The pressure of the springs 81 is such that the elements 80 are urged outwardly with a slight force, the force being just great enough to hold the ends 78V of. the sheet 22, againstinadvertent dislodgement and yet' permit them to bereadily slipped sidewise orwitli` drawn simply. b y tinger pressure on the strip 22.`

The centrifugalweights 80 are pivotally attachedl to the end plates 70 and 71' by pins 82. The plates 70 and 71 are relieved to provide spaces as. indicatedV at 83 and.

84' toV receive the members 80 on one side, while the spaces 84 on the. opposite side compensating for the weight reduction eiected by thepresence of the spaces 83.

As has been stated, when the drum is stationary the trailing ends 78 of'the sheet may be readily removed from the slots 76. However, whenY the drum starts up, the friction ofthe sandpaper on the. floor stretches and adjusts the sandpaper in place with the trailing. tips pushed' deeper into the slots. 76. Then as the; drum gains speed and is rotated Vat high speed, centrifugal force causes weights 80 to be forced outwardly,. clamping. the trailingends 78 securely in place.

Many advantages result from this arrangement. In the first place it is practically impossible manually to install the sandpaper 22 incorrectly so as to cause bulges or wrinkles. No tools are needed, and once the operator has hooked the grommet 77 over the hook 75 and inserted the two tips 78 in the slots 76, the job is completed. Even though the sandpaper 22 may be loose on the drum 11, the initial rotation of the drum as the motor is started automatically causes the paper 22v to locate itself correctly and hug the surface of the drum- 11, forcing the tips 78 all the way into the slots 76. is suspended from. a single central point 75, it is bound to roll onto the drum without wrinkling and the hugging action during the acceleration Viattens the paper against theY drum. The hugging actionl comes into play immediately after the drum starts to rotate, but the centrifugal forcev of thev weights 80 is not great enough to` prevent motion of the ends 78I into. the slots 76 until higherspeeds are reached. Stopping the drum releases the centrifugal forcev and the sandpaper can be removed by ones ngers only. Y

The springs 81 may be dispensed with, but. itisv preferred to use them for they hold the ends 78 lightly in place while the drum 11- ,is` stationary.

The shape of the leading edge of the strip 22 is complementary to the shape of the trailing edge. This results in two advantages. First, the stripsv 22' may be cut from a roll of material or large sheet without waste, and a much greater percentage ofthe abrasive` surface of each sheet is brought into contact with' the oorthan heretofore possible with conventional machines. Second,

the leading and trailing edges of the strip22 substantially meet when the strip is wound around thedrum 11, cover-v ing the drum completely Without overlapping. The strips.

22 are preferably made such length that only sufficient clearanceis left to compensate for manufacturing tolerances. The. leading and trailing edges need-not be cut on straight lines as long as they are respectively converging and diverging, following the same contour, and; do not overlapL when wound around the drum 11. However, it is. desirable that the strips 22 be symmetrical and supported at a central point, for otherwise they tend to move to the side of the drum 11 as it rotates, and there are no abrupt edges to cause chatter marks on the floor being sanded.

From the foregoing it will be seen that a very` superior arrangement for removably securing abrasive sheets to they drum has been provided. f The sheets are inexpensive to fabricate. and extremely simple to remove and apply. Furthermore, it is practically impossible-toinstallY a sheet improperly so that it may wrinkle or tear.

The iirst step is to install the properA grade of sandpaper on the drum 11 for the task at hand. The old sheet 22 is removed by withdrawingv the trailing ends 78 Sincethe strip 22- from the slots 76 and rotating the drum 11 until the hook is accessible so that the leading end' of the sheet 22V may be unhooked. The new sheet 22 is then hooked on the hook 75, and the drum is rotated in the drive direction, wrapping the sheet around the drum until the slots 76 are accessible. The trailing ends 78 are then inserted in the slots 76. Anytime the machine is stopped, it can be tilted back to take the weight' off of the drum.

It is preferred to have the drum lightly engaging the iioor when the motor 13 is started. The sandpaper immediately tightens and adjustsV itself incorrect position and, as the. motorcomes up to speed, the machine is moved back and forth over the oor. Y

From the foregoingdescriptiony it will be apparent that a greatly improved sander has been provided which is rugged in construction, easy to operate, and simple to maintain in adjustment. It will also be appreciated that the design may he modified and adapted to. other typesof Sanders than the particular modell described.

Accordingly, various changes and modications such as will present themselves to those familiar with the art may be made. without departing from. the spirit of thisV inventionwhose scope is dened by the following claims.

What is claimed is:

l'. In combination, a rotatable drum and a sheet of sandpapery having a sanding face and back side'wrapped around the drum with the sanding face disposed outwardly, one end of the sandpaper being pointed and the other end being swallowtailed to have two trailing. tips, means on the pointed end of said sheet for attaching same. to the drum, a pair of slots in the surface of said drum for receiving the tips of the other end with the sanding face engaging a rigid surface on the drum, and centrifugal means including an element lightly contacting the back side of said tips at said rigid surfaces to accommodate.

relative movement between the sheet and drum duringv slow rotation of the. drum and clamping said tips rigidly in place when said drum is rotated at sanding speeds.

2. In. combination, a rotatable drum and a sheet` of sandpaper wrapped around the drum, one endof the sandpaper being swallowtailed to have two trailing tips, ak pair of'. slots in; the surface of said drum for receiving the tips, and centrifugal means. including elements lightly engaging the: back side of said tipsl to press them out.`

wardly against, a portion of the drum and to accommodate relativegmovement between the sheet and drum during the initial rotationl of the drum at its starting point and said element clamping. said. tips rigidly'y in place when saidl drum is operating at'full speed when said' drum is rotated. Y

3:. In a sander, a rotatable drum, means on said drum midway between the ends thereof for supporting one end Y of. a piece ofVV sandpaper, a pair of slots in the lsurface ofV the. drum circumferentially spaced from said supporting means, andA means associated' with said slots for clampingthe trailing end of the sandpaper strip, said means in cluding. centrifugally responsive elements engaging said trailing end on the back face thereof in relative sliding relationship under an increasing clampingforce with increased speeds of saidY drum, and resilient members urging saidV elements into light engagement with said trailing end under' resting conditions of said drum.

4. In a sander, a rotatable drum, means onsaid drum midway.' between the ends thereof for supporting one end of a piece of sandpaper, said sandpaper being free to move axially along said means, a pair of slots in the surface of the drum4 circumferentially spaced from saidv supporting means and. adjacent the. ends of the drum, centrifugal means associated withsaid slots and engaging thel back side of said sandpaper in relative sliding relationship for clamping the `trailing end of the sandpaper sheet at working speeds of said drum and means for lightly holding said centrifugal means. in place subject to said freedom of movementunder resting conditions of the drum.

5. In a sander utilizing a exible. sheet. of abrasive. ma-

terial having a leading and a trailing edge, a cylinder rotatable about a fixed axis, means for pivotally securing the leading edge to the surface of the cylinder midway along the axis of rotation thereof, and means secured to the cylinder for clamping the trailing edge to the cylinder, said clamping means including resilient elements lightly engaging the back side of the trailing edge under resting conditions of the cylinder, and centrifugally influenced elements urged into clamping relationship with the trailing edge of the sheet in response to a predetermined centrifugal force whereby the exible sheet is rigidly clamped as the drum revolves at such speed as to apply a predetermined centrifugal force.

6. In a sander utilizing a exible sheet of abrasive material having a leading edge and a bifurcated trailing edge, a hollow cylinder rotatable about a xed axis, means secured to an outer surface of the cylinder for fastening the leading edge of the sheet to the cylinder at its axial midpoint, said cylinder having a pair of slots therein adjacent the periphery of the cylinder, said slots being adapted to receive the ends of the bifurcated trailing edge, a pair of centrifugally responsive arms pivotally mounted at one end Within the cylinder, the free end of each of said arms being adjacent one of the slots to engage comparatively lightly in relative sliding relationship the end of the trailing edge extending therethrough under resting conditions of the cylinder, and means for rotating the cylinder to produce a centrifugal force to rotate the arms outwardly whereby the arms clamp the ends against the under surface of the cylinder after a predetermined speed is attained.

7. In a sander utilizing a exible sheet of abrasive material a pointed leading edge and a trailing edge with a pair of spaced tips, a rotatable cylinder having an indented portion and a pair of slots therein, said indented portion being located in the surface of the cylinder midway along the axis of rotation, means secured in said indented portion for fastening the pointed edge to the cylinder, said slots being located directly opposite each other on the outer periphery of the cylinder, and means responsive to centrifugal force mounted within the cylinder adjacent each of the slots including elements lightly holding the trailing tips in place under resting conditions of the cylinder, said elements rigidly clamping the trailing tips of the sheet in place upon the cylinder reaching a predetermined rotational speed.

References Cited in the file of this patent UNITED STATES PATENTS 967,592 Wattles Aug. 16, 1910 1,030,538 Reed June 25, 1912 1,934,088 Ponselle Nov. 7, 1933 1,976,565 Kauiman Oct. 9, 1934 1,984,430 Reed Dec. 18, 1934 2,145,980 Hadwiger et al. Feb. 7, 1939 2,246,859 Pierce June 24, 1941 2,265,581 Stahl Dec. 9, 1941 2,414,366 Elze et al. Ian. 14, 1947 2,429,974 Anderson Nov. 4, 1947 2,456,488 Brown Dec. 14, 1948 2,492,849 Degen Dec. 27. 1949 

